The present invention relates in general to drive or knife shields used for forming tunnels or the like and employing a plurality of elongate drive members, sometimes called knives or planks. As is known, these drive members are arranged side-by-side in parallel relationship and are supported and guided for longitudinal displacement on one or more rigid frames. The drive members are advanced in the forward direction, either individually or in groups, in relation to the frame or frames usually by means of double-acting rams. In some drive shields the drive members have rear extensions, sometimes called tails, which project beyond the frame or frames in the rearward direction to form a rear shield. The rear extensions, which are often reduced in relation to the main bodies of the drive members, are used primarily to facilitate the construction of a tunnel lining for example by introducing fluid concrete or pre-cast concrete sections.
Where a drive shield is used in water-bearing strata it is also known to supply compressed air to the interior of the shield to maintain a certain constant pressure therein. This pressure then tends to prevent water seeping into the shield but the drive members should be provided with seals in order to close off the longitudinal gaps therebetween and maintain the pressure in the shield.
The seals also prevent water or the tunnel wall material or concrete used to form a lining from entering the shield. Examples of drive shields employing seals between adjacent pairs of drive members are described in U.S. Pat. No. 4,063,425. Since the drive members move relative to one another the seals are usually subjected to sliding friction and considerable wear can result. Nevertheless it is necessary to provide a tight frictional contact to provide the necessary sealing effect.
A general object of this invention is to provide an improved sealing means for the drive members of a drive shield.